Sulfurous acid

Sulfurous acid
Names
	IUPAC name Sulfurous acid
	Other names Sulfuric(IV) acid; Thionic acid; Sulfinic acid
Identifiers
CAS Number	7782-99-2 ;
3D model (JSmol)	Interactive image; Tautomer: Interactive image;
ChEBI	CHEBI:48854 ;
ChEMBL	ChEMBL1161699 ;
ChemSpider	1069 ;
ECHA InfoCard	100.029.066
EC Number	231-973-1;
Gmelin Reference	1458
KEGG	C00094 ;
PubChem CID	1100;
UNII	J1P7893F4J ;
CompTox Dashboard (EPA)	DTXSID7042435 ;
	InChI InChI=1S/H2O3S/c1-4(2)3/h(H2,1,2,3) Key: LSNNMFCWUKXFEE-UHFFFAOYSA-N ; InChI=1/H2O3S/c1-4(2)3/h(H2,1,2,3) Key: LSNNMFCWUKXFEE-UHFFFAOYAJ;
	SMILES O[S](=O)O; Tautomer: O[S+](O)[O-];
Properties
Chemical formula	H2SO3
Molar mass	82.07 g/mol
Acidity (pKa)	1.857, 7.172
Conjugate base	Bisulfite
Hazards
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H314, H332
Precautionary statements	P260, P261, P264, P271, P280, P301+P330+P331, P303+P361+P353, P304+P312, P304+P340, P305+P351+P338, P310, P312, P321, P363, P405, P501
Flash point	Non-flammable
Safety data sheet (SDS)	ICSC 0074
Related compounds
Related compounds	Sulfur dioxide; Sulfuric acid; Selenous acid
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Sulfuric(IV) acid (United Kingdom spelling: sulphuric(IV) acid), also known as sulfurous (UK: sulphurous) acid and thionic acid, is the chemical compound with the formula H₂SO₃.

Raman spectra of solutions of sulfur dioxide in water show only signals due to the SO₂ molecule and the bisulfite ion, HSO−3. The intensities of the signals are consistent with the following equilibrium:

SO₂ + H₂O ⇌ HSO−3 + H⁺ K_a = 1.54×10⁻²; pK_a = 1.81.

¹⁷O NMR spectroscopy provided evidence that solutions of sulfurous acid and protonated sulfites contain a mixture of isomers, which is in equilibrium:

[H−OSO₂]⁻ ⇌ [H−SO₃]⁻

Attempts to concentrate the solutions of sulfurous acid simply reverse the equilibrium, producing sulfur dioxide and water vapor. A clathrate with the formula 4SO₂·23H₂O has been crystallised. It decomposes above 7 °C.

Names


IUPAC name Sulfurous acid
Other names Sulfuric(IV) acid Thionic acid Sulfinic acid
Identifiers
CAS Number	7782-99-2^Y
3D model (JSmol)	Interactive image Tautomer: Interactive image
ChEBI	CHEBI:48854^Y
ChEMBL	ChEMBL1161699^Y
ChemSpider	1069^Y
ECHA InfoCard	100.029.066
EC Number	231-973-1
Gmelin Reference	1458
KEGG	C00094^Y
PubChem CID	1100
UNII	J1P7893F4J^Y
CompTox Dashboard (EPA)	DTXSID7042435
InChI InChI=1S/H2O3S/c1-4(2)3/h(H2,1,2,3)^Y Key: LSNNMFCWUKXFEE-UHFFFAOYSA-N^Y InChI=1/H2O3S/c1-4(2)3/h(H2,1,2,3) Key: LSNNMFCWUKXFEE-UHFFFAOYAJ
SMILES O[S](=O)O Tautomer: O[S+](O)[O-]
Properties
Chemical formula	H₂SO₃
Molar mass	82.07 g/mol
Acidity (pK_a)	1.857, 7.172
Conjugate base	Bisulfite
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H314, H332
Precautionary statements	P260, P261, P264, P271, P280, P301+P330+P331, P303+P361+P353, P304+P312, P304+P340, P305+P351+P338, P310, P312, P321, P363, P405, P501
Flash point	Non-flammable
Safety data sheet (SDS)	ICSC 0074
Related compounds
Related compounds	Sulfur dioxide Sulfuric acid Selenous acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is ^YN ?) Infobox references